The present invention relates to a switchable valve train for gas-exchange valves of internal combustion engines with a rocker arm device, in which a rocking motion about a rocking arm axis can be introduced by at least one cam, tappet, or the like, wherein this rocking motion can be transmitted to at least one valve, wherein the rocker arm device is formed from at least one cam lever part in working connection with the cam and a valve lever part in working connection with the valve and the lever parts are supported so that they can rock about the rocker arm axis.
Switchable valve trains are used to turn off individual valves with respect to their activation, so that these are set predominantly out of operation as a function of the operating point of the internal combustion engine. The operation of the valves is realized by rocker arm devices executing a rocking motion about a rocker arm axis. The rocker arm device motion is introduced by a cam, tappet, or the like, into a rocker arm device, wherein in connection with the use of a cam drive, the rocker arm device has at least one part, which is in working connection with the cam, and includes another part, which is in working connection with the valve. Therefore, the rocker arm device can be divided into a cam lever part and a valve lever part, which usually have a uniform construction with respect to structure and material and thus are locked permanently to each other in rotation. The valve executes a lifting motion, which can be activated in different ways either with respect to its control times or with respect to the size of the valve lift. For this purpose there exist special cam drives, which make the valve lift variably adjustable or also the opening and closing times of the valves variable through changing the geometry of the interacting components relative to each other.
From Patent publication DE 42 38 325, a switchable valve train according to the class for gas-exchange valves of internal combustion engines is known with a rocker arm device. Here, a driving device is disclosed that can be switched on and off with drivers constructed as balls. The driving device is arranged between the rocker arm device and a tappet element, which introduces the rocking motion into the rocker arm. If the driving device is turned off, then the motion of the tappet element is not transmitted to the rocker arm. Only when the ball elements engage is there a positive-fit connection between the tappet element and the rocker arm, so that the motion is transmitted. The ball elements engage in counter contours formed in the rocker arm itself. Through the use of a locking body, the balls are held in the counter contours in the closed position, so that a positive fit is formed. The locking body, which can be activated by fluids, has a groove geometry, so that when the locking body is activated, the groove geometry can be brought into alignment with the ball elements in such a way that the ball elements engage in the groove geometry and are thus guided out of the counter contours in the rocker arm. Thus, the released position of the driving device is generated, so that the motion is no longer transmitted.
The switchable valve trains known from the state of the art have the problem that they are formed from a plurality of individual parts, wherein the arrangement of the driving device is exposed to large dynamic loads. Furthermore, the driving device is designed merely for turning a valve on and off, so that alternating activation of a valve using several cams with different constructions is not possible.
Therefore, it would be desirable to provide a switchable valve train for gas-exchange valves of internal combustion engines, wherein this valve train has a simple construction and allows the operation of a valve by various cams.